The present invention relates to a burner operable in fire and flue modes and to a method of supplying heat to a chamber wherein first and second burners are arranged to direct hot products of combustion into the chamber, fuel is supplied to said burners alternately, during the supply of fuel to the first of said burners, air is supplied through the first burner, hot products of combustion pass from the chamber into the second burner, heat is extracted from products of combustion which have left the chamber and is stored in heat storage means and wherein, during the supply of fuel to the second burner, air is passed through the heat storage means associated with that burner to receive heat therefrom, the heated air being mixed with fuel by the second burner and hot products of combustion passing from the chamber through the first burner and heat being extracted from the products of combustion by heat storage means associated with the first burner. The chamber may contain workpieces which are to be heated. The workpieces may be moved continuously or intermittently through the chamber. Alternatively, the workpieces may be heated in a batch process. Alternatively, a fluid which is to be heated may be directed through ducts which extend through or are incorporated into the walls of the chamber. In a further alternative, heat may be transferred through the walls of the chamber from the products of combustion to material which is to be heated.
In U.S. Pat. No. 4,604,051 issued Aug. 5, 1986 to Davies et al there is disclosed a burner operable in fire and flue modes and in which there is incorporated heat storage means for storing heat extracted from products of combustion during the flue mode and imparting that heat to combustion air during operation in the fire mode.
The burner disclosed by Davies et al has a tubular structure extending along and defining an axis of the burner. In the tubular structure, there is defined a fuel-supply duct for supplying fuel to a nozzle at one end of the tubular structure. The heat store is in the form of a conical bed which surrounds and is spaced from the burner axis. The bed is confined between radially inner and outer perforated walls, both of which are conical in shape and which diverge from the burner axis in a direction towards the nozzle. A conical space between a radially outer, impermeable wall of the tubular structure and the radially inner, permeable wall of the bed receives products of combustion which enter the burner in the flue mode. These products of combustion flow in a generally radially outward direction through the bed and then along an outer, conical chamber towards an outlet from the burner.
Davies et al teach the provision of a bed which is composed of fairly small particles. Small particles have a high surface area relative to volume and therefore provide good heat exchange with the flue gases and with the combustion air. However, a bed composed of small particles provides a relatively high resistance to the flow of gases through the bed, as compared with a heat store defining relatively large passages for the flow of gases. In order to avoid an excessively large pressure drop through the bed, the bed proposed by Davies et al is thin, as measured in the radial direction, so that the path followed by gases through the bed is short. In consequence of this, the cycle time must be short and a cycle time of 15 seconds is taught in the Davies et al patent.
At the end of each half cycle, there must be a delay between the interruption of the supply of fuel to one burner and the resumption of the supply of fuel to the other burner. Typically, the duration of this delay must be several seconds. With a cycle time of 15 seconds, this represents a substantial proportion of each cycle so that the heat output from the burners is substantially less than would be the case if one or other of the burners was firing throughout the entire cycle.
In U.S. Pat. No. 4,355,973 issued to John M. Bailey on Oct. 26, 1982, there is disclosed a regenerative burner for firing into a radiant heating tube. A cylindrical regenerator body is fitted into a cylindrical end portion of the tube. In an alternative arrangement disclosed by Bailey, several annular regenerator elements are arranged in a single row along the end portion of the tube with a fuel pipe extending through the centre of each element. In each of these cases, the outside diameter of the regenerator body or elements corresponds to the internal diameter of the tube, so that the regenerator body and elements are supported by their respective tubes.
A similar form of regenerator body is disclosed in U.K. patent No. 2,128,724 granted Nov. 13, 1985 to British Gas Corporation. The regenerator body disclosed in this patent is a monolithic refractory block through which a multiplicity of axial channels extend.
U.S. Pat. No. 2,399,609 issued to E. Wainer on Apr. 30, 1946 also discloses a pair of regenerators associated with a radiant tube. In this case, the tube is vertical and one regenerator is arranged vertically below a lower end of the tube. The other regenerator is arranged horizontally and communicates with the upper end of the tube through a duct which defines a right angle bend. Fuel is injected laterally into respective chambers communicating at one of their ends with the interior of the radiant tube and at their other ends with the respective regenerator.